Where is the signal we have at the moment . Z-1 – means that we take the previous value of the signal (moment (n-1)). , - are the filter coefficients.
Filter performs zero-phase digital filtering by processing the input data in both the forward and reverse directions. After filtering in the forward direction, it reverses the filtered sequence and runs it back through the filter. The resulting sequence has precisely zero-phase distortion and double the filter order. filter minimizes start-up and ending transients by matching initial conditions, and works for both real and complex inputs. Note that filter should not be used with differentiator and Hilbert FIR filters, since the operation of these filters depends heavily on their phase response.